Our microarray analysis unexpectedly revealed that other metabolic pathways are regulated in response to iron availability. The iron-dependent enzyme glutamate synthetase is also transcriptionally down-regulated in response to iron deprivation, and we have characterized the transcriptional control regions of this gene to identify the iron-responsive sequences. To identify the transcription factor that controls the iron-dependent activation of GLT1, we are carrying out screens for genes that stimulate GLT1 expression under conditions of iron deprivation. [unreadable] In some yeast species, such as Pichia guillermondii, the biosynthesis of riboflavin is activated in response to iron deficiency. In collaboration with the laboratory of Yuriy Boretsky at the Institute of Cell Biology, NAS, Ukraine, we are developing tools to study gene function in this industrially important yeast, and we have identified a transcription factor that is required for the induction of riboflavin biosynthesis.